在这项工作中,使用DFT理论水平进行了全面的从头算量子化学计算,以表征α-的两个稳定对称构象的稳定相互作用(H键和超共轭效应),β-,和γ-环糊精(CD)。为此,我们用“分子中的原子”(AIM)分析了电子密度,“自然键轨道”(NBO),以及三维和希尔伯特空间中的能量分解方法(CECA)。我们还计算了H键长和OH振动频率。在每一张被调查的CD里,量子化学描述符表征了伯OH(或羟甲基)和仲OH基团的H键之间的相互作用的强度,通过比较相同的量计算乙二醇,α-d-葡萄糖(α-d-Glcp)和水簇作为参考系统。通过使用这些外部标准,我们可以更定量地表征这些键的性质(例如,强度)。我们已经证明,单位内H键的键临界点(BCP)在环糊精中不存在,类似于α-d-Glcp和乙二醇。相比之下,CECA分析表明,相互作用的O...H原子之间存在交换(键状)相互作用。因此,交换相互作用是指化学键,即两个原子之间的H键,与BCP不同,这是不适合它的检测。
In this work, comprehensive ab initio quantum chemical calculations using the DFT level of theory were performed to characterize the stabilization interactions (H-bonding and hyperconjugation effects) of two stable symmetrical conformations of α-, β-, and γ-
cyclodextrins (CDs). For this purpose, we analyzed the electron density using \"Atom in molecules\" (AIM), \"Natural Bond Orbital\" (NBO), and energy decomposition method (CECA) in 3D and in Hilbert space. We also calculated the H-bond lengths and OH vibrational frequencies. In every investigated CD, the quantum chemical descriptors characterizing the strength of the interactions between the H-bonds of the primary OH (or hydroxymethyl) and secondary OH groups are examined by comparing the same quantity calculated for ethylene glycol, α-d-glucose (α-d-Glcp) and a water cluster as reference systems. By using these external standards, we can characterize more quantitatively the properties of these bonds (e.g., strength). We have demonstrated that bond critical points (BCP) of intra-unit H-bonds are absent in
cyclodextrins, similar to α-d-Glcp and ethylene glycol. In contrast, the CECA analysis showed the existence of an exchange (bond-like) interaction between the interacting O…H atoms. Consequently, the exchange interaction refers to a chemical bond, namely the H-bond between two atoms, unlike BCP, which is not suitable for its detection.